1. Field of the Invention
This invention relates to a dry process, silver salt photosensitive member having a high sensitivity in a near infrared region and a high contrast and also to a method for forming an image with the dry process, silver salt photosensitive member.
2. Related Background Art
Silver halide photographic processes so far used are distinguished in the photosensitivity, gradation, etc., as compared with other photographic processes, but their treatments are complicated, because treatments such as fixation, bleaching, etc. must be carried out by wet process and also have disadvantages in the mechanization of the treatments. Many attempts to form an image by dry process in place of the silver halide photographic processes have been so far made.
A method for forming an image with a heat-developable, photosensitive material, whose development is carried out by heat treatment, has been proposed as a particularly distinguished method for forming an image by dry process, as compared with the conventional methods for forming an image. For example, Japanese Patent Publication No. 43-4924 discloses a heat-developable photosensitive material comprising an organic silver salt and silver halide in catalytic contact with organic silver ions. Similar photosensitive materials are also disclosed in Japanese Patent Publication No. 44-26582 and Japanese Patent Laid Open No. 46-6074.
Besides the foregoing methods, heat-developable photosensitive materials, which are heated before image exposure to activate the material into a photosensitive state, and again heated wholly, after the image exposure, to form a developed image, and a method for preparing these materials, where the heat-developable photosensitive materials comprise a heat-developable photosensitive member containing no silver halide or contain silver halide but having no photosensitivity at all, have been also proposed, for example, in Japanese Patent Publications Nos. 51-29829, 53-41067 and 54-5687.
The heat-developable photosensitive materials are used in the image communication field and medical fields and also as practical photosensitive materials as computer outputs, etc., with the advantage that the image formation is carried out by dry process treatments without any wet process step.
The heat-developable photosensitive materials have a high photosensitivity and an easy photosensitization to the visible region because silver halide is used as a photosensitive element, and thus have been also used in a recording system using a gas laser having a transmission wavelength in the visible region such as He-Ne laser, Ar ion laser, etc. as a beam source.
Recently, a semiconductor laser has been developed as a beam source of lower cost, smaller size and lighter weight with a highly efficient output, as compared with a gas laser source, and practically used in the fields of optical disks such as compact disks, laser printers, etc. Particularly, AlGaAs-based laser having a transmission wavelength of 780 nm has been widely used recently. Thus, systematizing the compact dry process image recording with higher performance and lower cost can be expected with such a laser beam source providing the advantages of lower cost, smaller size and lighter weight and such heat-developable photosensitive materials.
However, since a merocyanine sensitizing pigment is used in the heat-developable photosensitive materials, spectral sensitization to the near infrared region is hard to obtain, and thus it is inevitable to use said He-Ne laser or a visible light gas laser such as Ar ion laser. This is because the merocyanine pigments disclosed in Japanese Patent Publication No. 49-18808 become considerably unstable when the ethylene chain is extended to absorb light of long wavelength.
Cyanine pigments used in silver halide photosensitive materials for the ordinary wet process treatment have a low sensitizing efficiency in the dry process treatment and thus have been regarded as unsuitable for the dry process silver salt photosensitive member.